An ink jet printer of the so-called "drop-on-demand" type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels where power pulses are used to cause the droplets of ink to be expelled, as required, from orifices or nozzles at the ends of the channels.
In a thermal ink jet printer, the power pulses that result in a rapidly expanding gas bubble to eject the ink from the nozzle are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by voltage pulses to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse. The ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel orifice and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
One particular form of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The nozzles in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicularly to the line of carriage movement, by a distance equal to the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an ink jet printer, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the nozzles. Maintenance and/or priming stations for the printheads of various types of ink jet printer are described in, for example, U.S. Pat. No. 4,855,764; 4,853,717 and 4,746,938 while the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
It has been found that before the printing operation begins it is necessary to draw ink through the printhead nozzles to thereby fill the channels and nozzles with ink so that printing can begin with accurate placement of the ejected ink upon the medium. It has also been found that under certain conditions the ink channels or nozzles will become clogged with debris or with dried ink. In such a situation, the printhead must be primed to remove the unwanted material by vacuum priming. In vacuum priming, a priming element is placed against the face of a printhead to cover the nozzles. A vacuum is applied to the nozzles through the priming element and ink is drawn from the printhead, through the priming element, and to a waste container. The priming element is typically made of a flexible and resilient material such as rubber.
In U.S. Pat. No. 4,567,494 to Taylor, a nozzle cleaning and priming apparatus for thermal ink jet printers is described. A hollow cylindrical suction cup includes a drain pipe for connection to a suction tube. A second cup made of foam is positioned within the hollow of the cup. The suction tube pulls ink from the printhead and through the foam cup under the application of a vacuum.
U.S. Pat. No. 4,881,085 to Gibson et al. describes a manually operated cleaning tool for use in a liquid ink jet printing apparatus. A vacuum head is used to remove excess printing liquid from the exposed face of an orifice plate. The vacuum head includes a solid vacuum block which has a fluid receiving chamber. An elastomeric member is bonded to the inside surface of the fluid chamber.
U.S. Pat. No. 4,947,191 to Nozawa et al. describes an ink jet recording apparatus including a capping unit for covering the plural discharging openings for an ink jet head and suction means for sucking ink from the discharging openings through the capping means.
U.S. Pat. No. 4,952,947 to Kyoshima describes an ink discharge recovery device having a cap capable of covering a recording liquid discharge surface and a suction means for sucking ink and/or air from the plurality of discharge openings through the cap.
U.S. Pat. No. 5,040,000 to Yokoi describes an ink jet recording apparatus having an ink recovery system. The ink recovery system includes a cap member for suction recovery, a suction pump for sucking, a cleaning member for cleaning a discharge sur-face of a recording head and a driving member for driving the cleaning member.
U.S. Pat. No. 5,055,856 to Tomii et al. describes a capping device for an ink jet printer. The ink capping device includes a cap for sealing the ink outlet portion of an ink jet printhead, a suction device for maintaining a proper ink level within the printhead and a valve to regulate pressure within the print head.
U.S. Pat. No. 5,138,334 to Rowe et al. describes an arrangement for cleaning the face of ink jet printhead. A suction chamber is directed towards but spaced apart from the the printhead face to draw air over the printhead face to remove contamination such as ink and paper fibers.
U.S. Pat. No. 5,164,748 to Katayanagi et al. describes a suction recovery device with a cap having a communicating member to aid suction. The suction recovery device includes a cap having an ink suction portion and an ink exhaust path communicating with the ink suction port.
U.S. Pat. No. 5,210,550 to Fisher et al. describes a maintenance station for an ink jet printer. The maintenance station provides for priming of the printhead as well as maintaining a humid environment to prevent ink from drying out in the printhead orifices. A resilient seal means with lips contacts the printhead face during priming and cleaning.
U.S. Pat. No. 5,250,962 to Fisher et al. describes a movable priming station for use with an ink jet printer. The movable priming station includes a vacuum port. The vacuum port can be provided with a suction tip which can be oval shaped.
Japanese Publication No. 62-271749 describes a seal cap having a cavity wall having a recessed part capable of holding a recording liquid. Under a capped condition, the seal cap prevents ink coagulation at an ink ejecting port.
One problem encountered with many prior priming stations is that fluid-tight sealing between the stations and the printhead faces containing the droplet ejecting orifices causes high negative pressures within the priming stations under the application of a vacuum to prime or clean the droplet ejecting orifices. Such an arrangement can cause the collapse of certain elements of the priming station or may necessitate the use of a vacuum which supplies less negative pressure than desirable for the priming or cleaning of droplet ejecting orifices. The priming element of the present invention is less susceptible to collapse under the application of negative pressures typically used for ink jet nozzle priming or cleaning and allows for the application of increased negative pressure to a printhead for priming and cleaning.